Because of their excellent color, hardness and solvent and chemical resistance, aminoplast resinous compositions, particularly melamine-formaldehyde resinous compositions, have found many uses in the plastics, molding, coating and laminating fields. These resins give a thorough impregnation and thereby insure a complete bond when employed in the production of laminates. Resistance to discoloration due to heat and light is also realized.
For many years, these resinous compositions have been used in the production of decorative, high pressure laminates wherein a plurality of phenolic resin impregnated kraft paper sheets have been used as a laminate core to which is bonded, at 310.degree. F. and 1600 psi, melamine-formaldehyde resin impregnated decorative and overlay sheets. These laminates are then bonded to a rigid substrate and used as partitions, walls, doors, table and counter tops, etc.
More recently there has been a growing demand for a laminated panel which can readily be fabricated into furniture, kitchen cabinets and the like. These panels are produced by applying a single melamine-formaldehyde resinous composition impregnated decorative sheet to a particleboard substrate at much lower pressure and temperature, i.e., 160.degree. C. and 325 psi. Consequently, these laminate panels have been designated "low pressure" panels as distinguished from the "high pressure" laminates discussed above.
Low pressure panels have been very favorably accepted by the industry, and as a result, extensive research has been recently undertaken to improve these panels. One area in the panel production which has not proven to be as successful as would be desired comprises the inability of the impregnated paper to be stored over a period of time which would enable the production of many sheets at one time, thereby obviating the necessity of producing said sheets at very short time intervals. That is to say, when the paper sheets are produced, it would be advantageous to be able to produce many sheets at one time for storage and later use. However, attempts to produce impregnated sheets in this manner have resulted in products which are only storage stable for 4-6 weeks. As a result, sheet production must also be effected every 4-6 weeks. Accordingly, if a new .beta.-staged, impregnated paper sheet could be devised which had a longer storage life and resulted in panels which had an increased resistance to stress-cracking, particularly at low humidity, a long felt need would be satisfied.